In circuit design, passive components refer to components that are not capable of power gain such as, for example, capacitors, inductors, resistors, diodes, transmission lines and transformers. In circuit design for communications systems, for example, a large area of the board is taken up by passive devices. For example, 90-95% of components in a cellular telephone are passive components, taking up approximately 80% of the total transceiver board, which accounts for about 70% of the cost. To reduce the space taken up by the passive devices, very small discrete passive components and the integration of the passive components are under development.
Multi-chip module, system on chip (SOC)/system on package (SOP) in which the passives and interconnects are incorporated into the carrier substrate offer an attractive solution to further increase the integration. For example, SOC is a fully integrated design with RF passives and digital and analog circuits on the same chip. Their operation on CMOS grade silicon, however, is degraded by the high loss of transmissions lines and antennas. On the other hand, BiCMOS technologies present a cost effective option to realize highly integrated systems combining analog, microwave design techniques, transmission lines and other passive components.
In any event, many efforts have been made to reduce the size of the passive devices. For example, to reduce the space taken up by the passive components, discrete passive components have been replaced with on-chip passive components. However, size reduction of passive components may depend at least in part on the further development of on-chip interconnects, such as slow-wave coplanar waveguide (CPW) structures, for microwave and millimeter microwave integrated circuits (MICs), microwave and millimeter monolithic microwave integrated circuits (MMICs), and radiofrequency integrated circuits (RFICs) used in communications systems. In particular, interconnects that promote slow-wave propagation can be employed to reduce the sizes and cost of distributed elements to implement delay lines, variable phase shifters, branchline couplers, voltage-tunable filters, etc. However, advanced coplanar waveguide structures are needed for radio frequency and microwave integrated circuits to serve as interconnects that promote slow-wave propagation, as well as related design structures for radio frequency and microwave integrated circuits.
Accordingly, there exists a need in the art to overcome the deficiencies and limitations described hereinabove.